This proposal will address a fundamental gap in the social epidemiology literature on the HIV risk behavior and substance use trajectories of recent Latino immigrants. The long term goal is to contribute to reduction and elimination of Latino health disparities in HIV/AIDS and substance abuse. The objective of this particular research project is to determine how the HIV risk behavior of Latino immigrants who have been in the U.S. for less than one year are influenced by pre-immigration assets (e.g., Latino cultural assets, social capital, and religious assets), early in their immigration process. The central hypothesis is that the relationship between pre-immigration assets and post-immigration HIV risk behaviors will be mediated by post-immigration acculturation related stress and substance use over a two-year time period in the U.S. while controlling for pre-immigration HIV and substance use risk behaviors. This hypothesis will be tested by three specific aims: (1) examine the influence of pre-immigration assets on post-immigration HIV risk behaviors among recent Latino immigrants over time; (2) identify the effects of pre-immigration assets on post-immigration acculturation related stress and substance use among recent Latino immigrants over time; (3) investigate the relationship between pre-immigration assets, and post-immigration acculturation related stress, substance use, and HIV risk behaviors over time. The study design involves three waves of data collection (a baseline and two follow ups) spaced twelve months apart over a period of two years. The study will be conducted in Miami-Dade County, the only county in the U.S. with an immigrant majority (51%). The approach is innovative, because it acknowledges the importance of pre-immigration factors in predicting post-immigration HIV risk behavior, an often neglected area in the literature. In addition, the study focuses on a sample of 18 to 34 years olds (a high risk group both for HIV and substance use) during their early stages of immigration. It is the first longitudinal study to investigate the HIV and substance use risk behavior of this group of recent Latino immigrants. The proposed research is significant, because it can identify important predictors of HIV and substance use behavior trajectories for Latino immigrants in the U.S. and can provide the knowledge needed to develop new HIV and substance abuse prevention programs or enhance existing programs that identify, sustain and incorporate assets of Latino populations into culturally grounded intervention. Relevance to Health Disparities: Ethnic and racial minorities, especially African Americans and Latinos, are disproportionately affected by the HIV/AIDS epidemic. The need for developing HIV and substance abuse prevention programs is unquestionable for Latino immigrants who may be at-risk as they become increasingly acculturated to the U.S. society.